Electronic expansion valve and superheat control in an hvac system

ABSTRACT

An EXV (electronic expansion valve) control system includes an EXV controller for controlling an EXV within the refrigerant loop of an HVAC system. The EXV controller implements a master control algorithm that includes a plurality of sub-control algorithms and an initial series of branching decision points to determine the current mode of operation and to execute select sub-control algorithms corresponding to the current mode of operation, while not executing the sub-control algorithms corresponding to the other modes of operation. The sub-control algorithms implement various combinations of PID (Proportional Integral Derivative) control and feed-forward control, the results of which can be mapped to specific control instructions for the EXV.

FIELD OF THE INVENTION

The present invention is generally directed to an HVAC (Heating,Ventilating, and Air Conditioning) system. More specifically, thepresent invention is directed to control systems and algorithms forcontrolling an HVAC system.

BACKGROUND OF THE INVENTION

An HVAC system typically includes an evaporator coil, a condenser, anaccumulator, a condensor, and a metering device. The components areinterconnected by pipes or tubing, and separate fans move air across theevaporator coil and the condenser. A refrigerant is in various phases asit flows through the air conditioning components. Circulatingrefrigerant vapor enters the compressor and is compressed to a higherpressure, resulting in a higher temperature as well. The compressedrefrigerant vapor is now at a temperature and pressure at which it canbe condensed and is routed through the condenser. In the condenser, thecompressed refrigerant vapor flows through condenser coils. A condenserfan blows air across the condenser coils thereby transferring heat fromthe compressed refrigerant vapor to the flowing air. Cooling thecompressed refrigerant vapor condenses the vapor into a liquid. Thecondensed refrigerant liquid is output from the condenser to theaccumulator where the condensed refrigerant liquid is pressurized. Thecondensed and pressurized refrigerant liquid is output from theaccumulator and routed through the metering device where it undergoes anabrupt reduction in pressure. That pressure reduction results in flashevaporation of a part of the liquid refrigerant, lowering itstemperature. The cold refrigerant liquid/vapor is then routed throughthe evaporator coil. The result is a mixture of liquid and vapor at alower temperature and pressure. The cold refrigerant liquid-vapormixture flows through the evaporator coil and is completely vaporized bycooling the surface of the evaporator coil and cooling air moving acrossthe evaporator coil surface. The resulting refrigerant vapor returns tothe compressor to complete the cycle.

A primary function of the metering device is to regulate the amount ofrefrigerant released into the evaporator thereby keeping superheat at asuperheat set point value, ensuring that the only phase in which therefrigerant leaves the evaporator is vapor, and, at the same time,supplying the evaporator coils with the optimal amount of liquidrefrigerant to achieve the optimal heat exchange rate allowed by thatevaporator. Superheating is the energy added to saturated gas, resultingin a temperature increase. During the evaporation of a liquidrefrigerant, the temperature depends only on the boiling temperature ofthat refrigerant. Increasing the temperature (superheating) is possibleonly after obtaining 100% vapor. Once the refrigerant has boiled to avapor then any temperature above and beyond the boiling point is knownas the superheat. In other words, superheat is any temperature of a gasthat is above the boiling point for that liquid. In general, superheat(temperature) is calculated as the difference between the measuredtemperature (output from the evaporator) and the current saturationtemperature, where the current saturation temperature is calculatedaccording to the measured pressure (output from the evaporator).Superheat provides a measure as to whether or not the correct amount ofrefrigerant is being fed into the evaporator. If the superheat is toohigh, then not enough refrigerant is being fed in. This can result inpoor system performance and loss of energy efficiency. However, if thesuperheat is too low, then there is a surplus of refrigerant being fedinto the evaporator. This result can be a sign that liquid refrigerantis entering into the compressor. Liquid refrigerant inside a compressorcan mix with oil at the bottom of the compressor casing. This can resultin poor lubrication to the compressor and may result in prematurefailure.

The metering device includes an expansion valve, which regulates theamount of refrigerant released into the evaporator. One type ofexpansion valve is a thermal expansion valve, often abbreviated as TEV,TXV, or TX valve. The TXV is configured to maintain a stable level ofsuperheating inside the evaporator under all conditions by adjusting themass flow of refrigerant in response to the evaporator load. Flowcontrol, or metering, of the refrigerant is accomplished by use of atemperature sensing bulb that causes an orifice in the valve to open orclose depending on a temperature of the refrigerant. TXVs are populardue to their simplicity and availability, and their relatively goodsensitivity and accuracy in regulation. The large choice of expansionvalve sizes and bulbs means the capacity and temperature ranges are verygood. A disadvantage of TXVs is the necessity for relatively highsuperheating, which negatively effects the evaporation process.

Another type of expansion valve is an electronic expansion valve (EXV).An EXV is generally considered an improvement over the TXV. EXVs aremore sophisticated and allow the HVAC system to operate more accuratelyand efficiently than TXVs. EXVs include a stepper motor coupled to avalve head. Step-wise action of the stepper motor enables opening orclosing of the valve according to control instructions received by thestepper motor from an EXV controller. Benefits to using an EXV includeprecise control, fast, and accurate response to load change, wider partload variation than a TXV, maintains maximum capacity control even atpart loads, and more accurately injects the right amount of refrigerant,which all contribute to improved performance and reduced energyconsumption for the HVAC system.

SUMMARY OF THE INVENTION

Embodiments are directed to an EXV control system including an EXVcontroller for controlling an EXV within the refrigerant loop of an HVACsystem. The EXV controller implements a master control algorithm thatincludes a plurality of sub-control algorithms and an initial series ofbranching decision points to determine the current mode of operation andto execute select sub-control algorithms corresponding to the currentmode of operation, while not executing the sub-control algorithmscorresponding to the other modes of operation. The sub-controlalgorithms implement various combinations of PID (Proportional IntegralDerivative) control and feed-forward control, the results of which canbe mapped to specific control instructions for the EXV.

In an aspect, an HVAC system is disclosed that includes a refrigerantloop, a compressor, an evaporator, an electronic expansion valve, and acontroller. The refrigerant loop includes a refrigerant flowing within.The compressor is coupled to the refrigerant loop, and the evaporator iscoupled to the refrigerant loop. The electronic expansion valve iscoupled to the refrigeration loop to regulate a mass flow of therefrigerant into the evaporator. The controller is coupled to thecompressor and the electronic expansion valve. The controller isconfigured to receive data signals corresponding to one or morecompressor characteristics. The controller includes and is configured toexecute a master control algorithm to generate control signals forcontrolling the electronic expansion valve. The master control algorithmcomprises a plurality of sub-control algorithms and an up-frontevaluation algorithm, each of the plurality of sub-control algorithms isconfigured to determine a step adjustment of the electronic controlvalve. The master control algorithm executes the up-front evaluationalgorithm to determine a current operating mode according to thereceived compressor characteristics and then selectively executes asubset of the plurality of sub-control algorithms depending on thedetermined current operating mode. In some embodiments, the HVAC systemfurther comprises an external temperature sensor coupled to thecontroller and configured to sense a temperature external to the HVACsystem. In some embodiments, the controller is further configured toperform a feed-forward control by mapping the measured compressorcharacteristics and the sensed external temperature to a correspondingopen position of the electronic expansion valve. In some embodiments,the controller is further configured to receive data signalscorresponding to a pressure value at an output of the evaporator and atemperature value at the output of the evaporator. In some embodiments,the controller is further configured to perform a PID (ProportionalIntegral Derivative) control using the received pressure value and thereceived temperature value to adjust the open position of the electronicexpansion valve. In some embodiments, the master control algorithm isconfigured to selectively execute the plurality of sub-controlalgorithms depending on the determined current operating mode whilebypassing remaining sub-control algorithms corresponding tonon-determined current modes of operation. In some embodiments, thecurrent operating mode is one of a start-up mode, a compressor rpschange mode, and a load change mode. In some embodiments, the up-frontevaluation algorithm is configured to determine if the compressor is on,and then determine if the compressor is at start-up, which correspondsto the start-up mode, and then determine if there is a compressor rpschange, which corresponds to the compressor is change mode, and if thecompressor is on but neither the compressor is in start-up nor is therecompressor rps change then it is determined that the current operatingmode is the load change mode.

In another aspect, another HVAC system is disclosed that includes arefrigerant loop, a compressor, an evaporator, an electronic expansionvalve, and a controller. The refrigerant loop includes a refrigerantflowing within. The compressor is coupled to the refrigerant loop, andthe evaporator is coupled to the refrigerant loop. The electronicexpansion valve is coupled to the refrigeration loop to regulate a massflow of the refrigerant into the evaporator. The controller is coupledto the compressor and the electronic expansion valve. The controller isconfigured to receive data signals corresponding to one or morecompressor characteristics. The controller includes and is configured toexecute a master control algorithm to generate control signals forcontrolling the electronic expansion valve. The master control algorithmincludes a feed-forward sub-control algorithm that generates a stepadjustment of the electronic control valve based on the one or morecompressor characteristics to proactively adjust the electronic controlvalve. In some embodiments, the HVAC system further comprises atemperature sensor for sensing an external temperature, and the datasignals received by the controller further include an externaltemperature value. In some embodiments, the feed-forward sub-controlalgorithm generates the step adjustment based on the one or morecompressor characteristics and the external temperature value. In someembodiments, the master control algorithm comprises a plurality ofsub-control algorithms, the feed-forward sub-control algorithm is one ofthe plurality of sub-control algorithms. In some embodiments, the mastercontrol algorithm is configured to selectively execute a subset of theplurality of sub-control algorithms depending on a determined currentoperating mode, further wherein the current operating mode is determinedaccording to the compressor characteristics. In some embodiments, thecurrent operating mode is one of a start-up mode, a compressor rpschange mode, and a load change mode. In some embodiments, the subset ofthe plurality of sub-control algorithms corresponding to the start-upmode includes a first feed-forward control algorithm, a first PID(Proportional Integral Derivative) control algorithm, and a second PIDcontrol algorithm. In some embodiments, the master control algorithm isconfigured to execute the first feed-forward control algorithm toprovide a coarse-tuned first electronic expansion valve step adjustment,then to execute the first PID control algorithm to provide a fine-tunedsecond electronic expansion valve step adjustment, and then to executethe second PID control algorithm to provide a fine-tuned thirdelectronic expansion valve step adjustment. In some embodiments, thefirst PID control algorithm applies first gain factor values and thesecond PID control algorithm applies second gain factor values differentfrom the first gain factor values. In some embodiments, the subset ofthe plurality of sub-control algorithms corresponding to the compressorrps change mode includes a second feed-forward control algorithm, athird PID control algorithm, and the second PID control algorithm. Insome embodiments, the master control algorithm is configured to executethe second feed-forward control algorithm to provide a coarse-tunedfirst electronic expansion valve step adjustment, then to execute thethird PID control algorithm to provide a fine-tuned second electronicexpansion valve step adjustment, and then to execute the second PIDcontrol algorithm to provide a fine-tuned third electronic expansionvalve step adjustment. In some embodiments, the second PID controlalgorithm applies second gain factor values and the third PID controlalgorithm applies third gain factor values different from the secondgain factor values. In some embodiments, the subset of the plurality ofsub-control algorithms corresponding to the load change mode includes afourth PID control algorithm and the second PID control algorithm. Insome embodiments, the master control algorithm is configured to executethe fourth PID control algorithm to provide a fine-tuned firstelectronic expansion valve step adjustment and then to execute thesecond PID control algorithm to provide a fine-tuned second electronicexpansion valve step adjustment. In some embodiments, the data signalsreceived by the controller further include a pressure value at an outputof the evaporator and a temperature value at the output of theevaporator. In some embodiments, the controller is further configured toexecute a PID control algorithm using the received pressure value andthe received temperature value to adjust the electronic expansion valve.In some embodiments, the master control algorithm is configured to firstexecute the feed-forward control algorithm followed by the PID controlalgorithm.

BRIEF DESCRIPTION OF THE DRAWINGS

Several example embodiments are described with reference to thedrawings, wherein like components are provided with like referencenumerals. The example embodiments are intended to illustrate, but not tolimit, the invention. The drawings include the following figures:

FIG. 1 illustrates a schematic block diagram of the HVAC unit andconstituent components corresponding to air conditioning functionalityaccording to some embodiments.

FIG. 2 illustrates a simplified block diagram of the HVAC system of FIG.1 according to some embodiments.

FIG. 3 illustrates a functional block diagram for a PID controlalgorithm according to some embodiments.

FIG. 4 illustrates a functional block diagram of an algorithm utilizingboth PID control and feed-forward control according to some embodiments.

FIG. 5 illustrates a master control algorithm according to someembodiments.

FIG. 6 illustrates the start-up fast SH control algorithm of FIG. 5according to some embodiments.

FIG. 7 illustrates the rps change fast SH control algorithm of FIG. 5according to some embodiments.

FIG. 8 illustrates the load change fast SH control algorithm of FIG. 5according to some embodiments.

FIG. 9 illustrates the fine SH control algorithm of FIG. 5 according tosome embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present application are directed to an EXV controlsystem used in an HVAC system. Those of ordinary skill in the art willrealize that the following detailed description of the EXV controlsystem is illustrative only and is not intended to be in any waylimiting. Other embodiments of the EXV control system will readilysuggest themselves to such skilled persons having the benefit of thisdisclosure.

Reference will now be made in detail to implementations of the EXVcontrol system as illustrated in the accompanying drawings. The samereference indicators will be used throughout the drawings and thefollowing detailed description to refer to the same or like parts. Inthe interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application and business related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

In some embodiments, an HVAC system includes three sub-assemblies: anindoor air cycling section, a mechanical section, and an outdoor aircycling section. The indoor air cycling section, or simply “indoorsection”, cycles air from an interior area of a unit (e.g. indoors) andback out to the interior area. The outdoor air cycling section, orsimply “outdoor section”, cycles air from an area exterior to the unit(e.g. outdoors) and back out to the exterior area. The indoor section,the mechanical section, and the outdoor section can be integrated withina single device, e.g. an HVAC system, or can be separated as one, two,or three discrete modules coupled together. For example, in a split HVACsystem there are two modules, one module includes the indoor section andthe other module includes the outdoor section and the mechanicalsection. In an application where air conditioning cooling is performed,the indoor section functions as an evaporator section, and the outdoorsection functions as a condenser section. It is understood that the HVACsystem also can be used for heating, in which case the functionality ofthe indoor section and the outdoor section can be reversed from thatdescribed regarding an evaporator section and a condenser section.Subsequent discussion may be directed to air conditioning cooling andtherefore reference is made in those occurrences to an evaporatorsection having an evaporator coil and a condenser section having acondenser coil. It is understood that such description can be generallyapplied to an indoor section and an outdoor section that performs aheating function.

The evaporator section includes a heat exchanger, an air mover, andelectrical circuitry. In some embodiments, the heat exchanger includesan evaporator coil and interconnecting refrigerant tubing. In someembodiments, the air mover includes a motor and a fan, generallyreferred to as an indoor fan, i.e. a fan for the indoor section. In someembodiments, the electrical circuitry includes power wiring, controlwiring, and control/diagnostic sensors. The mechanical section includesrefrigerant loop components, in-line components, and electricalcircuitry including HVAC system control. In some embodiments, therefrigerant loop components include a compressor and a metering device,such as an electronic expansion valve. In some embodiments, the in-linecomponents include one or more valves, one or more filters, andinterconnecting refrigerant tubing. In some embodiments, the electricalcircuitry of the mechanical section includes HVAC system controls,electrical components, power wiring, control wiring, andcontrol/diagnostics sensors. The condenser section includes a heatexchanger, an air mover, an auxiliary heating component, air qualitycomponents, and electrical circuitry. In some embodiments, the heatexchanger of the condenser section includes a condenser coil andinterconnecting refrigerant tubing. The condenser section can alsoinclude an accumulator. In some embodiments, the air mover in thecondenser section includes a motor and a fan generally referred to as anoutdoor fan, i.e. a fan for the outdoor section. In some embodiments,the auxiliary heating component includes one or more resistive heatingelements. In some embodiments, the air quality components include an airfilter and ventilation components. In the some embodiments, theelectrical circuitry of the condenser section includes power wiring,control wiring, and control/diagnostic sensors.

FIG. 1 illustrates a schematic block diagram of an HVAC system 2 andconstituent components corresponding to air conditioning functionalityaccording to some embodiments. The HVAC system 2 includes an evaporatorsection 4, a mechanical section 6, and a condenser section 8. A heatexchanger 12 including an evaporator coil in the evaporator section 4 iscoupled to a compressor 18 via interconnecting refrigerant tubing andone or more valves 20. The compressor 18 is coupled to a heat exchanger28 including a condenser coil in the condenser section 8 viainterconnecting refrigerant tubing and the one or more valves 20. Theheat exchanger 28 also can include an accumulator (not shown) that iscoupled to the condenser coil via interconnecting refrigerant tubing.The heat exchanger 28 is coupled to a metering device 24 viainterconnecting refrigerant tubing, one or more valves, and filters 22.The metering device 24 is coupled to the heat exchanger 12 viainterconnecting refrigerant tubing. In this manner a refrigerant loop isformed, where the refrigerant loop includes the evaporator coil in theheat exchanger 12, the compressor 18, the condenser coil and theaccumulator in the heat exchanger 28, the metering device 24, and theinterconnecting pipes, valves, and filters. It is understood that thenumber and configuration of interconnecting refrigerant tubing, valves,and filters shown in FIG. 1 is for exemplary purposes only and thatalternative configurations are also contemplated for interconnecting theheat exchanger 12, the compressor 18, the heat exchanger 28, and themetering device 24. It is also understood that the direction ofrefrigerant flow can be one direction for cooling functionality (airconditioning) and the other direction for heating functionality.

An air mover 10 in the evaporator section 4 is coupled to the heatexchanger 12 to blow air over the evaporator coil, and an air mover 26in the condenser section 8 is coupled to the heat exchanger 28 to blowair over the condenser coil. A compressor controller 16 is coupled tothe compressor 18. In some embodiments, the compressor controller 16includes programmable logic circuitry and memory for executing controlalgorithms used to control operation of the compressor 18. In someembodiments, the compressor 18 is a variable speed compressor that canbe selectively controlled to operate at multiple different speeds (rpm).An HVAC unit controller 14 is coupled to the air mover 10, thecompressor controller 16, the one or more valves such as valves 20, themetering device 24, and the air mover 26. In some embodiments, the HVACunit controller 14 includes programmable logic circuitry and memory forexecuting control algorithms used to control operation of the HVACsystem 2 and corresponding components. Control signaling, indicated by“C” in FIG. 1 , is transmitted between the compressor controller 16 andthe compressor 18, and between the HVAC unit controller 14 and the airmover 10, the compressor controller 16, the one or more valves such asvalves 20, the metering device 24, and the air mover 26. In someembodiments, the compressor controller 16 can be integrated as part ofthe HVAC unit controller 14. Control/diagnostic sensors 30, 32, 34, 36can be used to sense various ambient conditions, such as temperature orhumidity, which are connected back to the HVAC unit controller 14 andcan be used to control the various components of the HVAC system 2. Highvoltage power, such as 120 VAC, is supplied to each of the air mover 10,the compressor controller 16, and the air mover 26. High voltage powercan be supplied from the compressor controller 16 to the compressor 18.High voltage power input is indicated by “H” in FIG. 1 . Low voltagepower is supplied to the unit controller 14. Low voltage power can beprovided via wiring labeled “C”. It is understood that alternative powersupply configurations are also contemplated.

The HVAC unit controller 14 is connected to a human-machine interface(HMI), also referred to as a user interface, that can be installed on afront side of the HVAC system. User interface with the HVAC unitcontroller 14 also can be made using an installation/service applicationincluded on a mobile device. The HVAC unit controller 14 is alsoexternally connected via a network connection, either wired or wireless.

In some embodiments, air filters are included as part of the evaporatorsection 4 and the condenser section 8. Air is drawn into the evaporatorsection 4, such, as from the unit in which the HVAC unit is installed,directed across the evaporator coil, and output from the evaporatorsection 4 back into the unit. The air filter can be positioned at an airintake portion of the evaporator section 4 such that air is filteredprior to being blown across the evaporator coil. Similarly, air is drawninto the condenser section 8, such as from outside the unit within whichthe HVAC unit is installed, directed across the condenser coil, andoutput from the condenser section 8 back outside the unit. The airfilter can be positioned at an air intake portion of the condensersection 8 such that air is filtered prior to being blown across thecondenser coil.

The evaporator section, the mechanical section, and the condensersection are described above as each having specific components. It isunderstood that this is for exemplary purposes only and that one or morecomponents may be positioned in different sections of the HVAC unit.

FIG. 2 illustrates a simplified block diagram of the HVAC system of FIG.1 according to some embodiments. In particular, FIG. 2 shows therefrigerant loop including the evaporator coil in the heat exchanger 12,the compressor 18, the condenser coil and the accumulator in the heatexchanger 18, the metering device 24, and the interconnecting pipes. Insome embodiments, the metering device 24 is implemented as an EXV. AnEXV controller 38 is coupled to control the EXV 24. In some embodiments,the EXV controller 38 includes programmable logic circuitry and memoryfor executing control algorithms and mapping tables used to controloperation of the EXV 24. In some embodiments, the EXV controller 38 canbe integrated as part of the HVAC unit controller 14. The EXV controller38 is coupled to a pressure sensor 40 and a temperature sensor 42 toreceive sensed pressure data and sensed temperature data, respectively,of the refrigerant output from the evaporator 12. The EXV controller 38also is coupled to the compressor 18 to receive compressor signals 44,which indicate various characteristics/conditions of the compressor 18.The compressor signals 44 can be a signal indicating a start-upcondition or a signal indicating a change in rps (revolutions persecond) of the compressor 18. In some embodiments, the start-upcondition signal is a binary value indicating whether or not thecompressor is in a start-up mode of operation. The start-up conditionindicates that the compressor has been turned on. In some embodiments,the change in rps signal is a binary value indicating whether or not therps of the compressor has been changed. In other embodiments, the changein rps signal provides an actual rps value of the compressor. The EXVcontroller 38 also is coupled to an outdoor temperature sensor 46 toreceive sensed outdoor temperature data. In some embodiments, theoutdoor temperature sensor 46 is positioned to measure an outdoorambient temperature. In other embodiments, the outdoor temperaturesensor 46 is positioned external to the HVAC system 2 or positionedexternal to a room or building being conditioned by the HVAC system 2.

In some embodiments, the EXV controller 38 includes a processing controlboard that includes programmable logic and control circuitry forreceiving and processing sensed data from a variety of different typesof sensors and the compressor, applying programmed logic and storedcontrol algorithms and mapping tables to determine control signaling forthe EXV 24, and generating and transmitting such determined controlsignaling to the EXV 24. In some embodiments, the processing controlboard includes a microprocessor, a CPU (central processing unit), orother similar type processing circuitry and/or integrated circuit forexecuting the control algorithms and mapping tables used to operate andcontrol the EXV 24. The control algorithms and mapping tables can bestored locally on the processing board or on a separate storage mediumaccessible by the processing circuitry. The mapping table definescontrollable actions to be taken, such as the steps to be applied to theEXV 24, based on the various received sensed data and compressorsignals.

The EXV controller 38 is configured to use the sensed pressure data, thesensed temperature data, the sensed outdoor temperature data, and/or thecompressor signals 44 to determine and send appropriate control signalsto the EXV 24. In some embodiments, the control signal sent to the EXV24 indicates an amount of “step” for adjusting the EXV, e.g. step theEXV open or closed by the number of steps and direction (positive foropen, negative for closed) indicated by the map, or that provides a stepvalue at which the EXV is to be set.

In some embodiments, the EXV controller 38 implements PID (ProportionalIntegral Derivative) control for generating the control signals sent tothe EXV 24. PID control is a known algorithm. PID control is a mechanismfor manipulating the EXV 24 according to measured temperature andpressure (output from the evaporator) to bring the current superheatcloser to the superheat set point. The PID control uses the measuredtemperature and pressure along with predefined gain values K_(P), K_(I)and K_(D) to calculate an EXV step (EXV control signal) for step-wiseopening or closing the EXV 24. The superheat set point is apredetermined constant value, typically set between 10 and 12 degreesfor air conditioning applications. If the actual current superheat isgreater than the superheat set point, then the energy consumption of theHVAC system increases resulting in reduced energy efficiency. Ingeneral, the higher the superheat, the lower the energy efficiency.However, the risk of damage to the HVAC system is inversely related tothe efficiency, meaning that the higher the efficiency (withcorresponding lower superheat set point) the greater the risk of damage.Therefore, a trade-off is made between energy efficiency and risk ofHVAC system damage to determine a superheat set point. The superheat setpoint value is determined during a calibration of the HVAC system duringproduction, and this predetermined superheat set point value is savedand used as a constant by the EXV controller during operation of theHVAC system.

FIG. 3 illustrates a functional block diagram for a PID (ProportionalIntegral Derivative) control algorithm according to some embodiments.PID control automatically adjusts a control output based on thedifference between the superheat set point and calculated currentsuperheat. To implement PID control, the temperature and pressure of therefrigerant output from the evaporator is sensed (measured) and thesensed data is used to adjust (regulate) the EXV 24 according to theresults of a PID control algorithm. The PID control algorithmcontinuously calculates an error value e(t) as the difference betweenthe calculated current superheat and the superheat set point, andapplies a correction based on proportional (P), integral (I), andderivative (D) terms to generate an EXV control signal u(t) that is sentto the EXV 24. In general, superheat is calculated as the differencebetween the measured temperature (output from the evaporator) and thecurrent saturation temperature, where the current saturation temperatureis calculated according to the measured pressure (output from theevaporator). In an exemplary application, the desired superheat isbetween 10 and 15 degrees. PID control attempts to minimize the errorover time by adjustment of the control signal u(t), such as the openingof the EXV, to a new value determined by a weighted sum of the controlterms P, I, and D. The distinguishing feature of PID control is theability to use the three control terms P, I, and D to influence the PIDcontrol output u(t) to apply accurate and optimal control of the EXV 24.The proportional term P is proportional to the current value of theerror value e(t). For example, if the error e(t) is large and positive,then the PID control output is proportionately large and positive,taking into account a proportional gain factor K_(P). The proportionalterm P is calculated by multiplying the error value e(t) by theproportional gain factor K_(P). Using proportional control alone resultsin an error between the superheat set point and the actual process value(calculated current superheat value) because it requires an error togenerate the proportional response. If there is no error, there is nocorrective response. The integral term I accounts for past values of theerror value e(t) and integrates these past values over time, indicatedin FIG. 3 as the box labeled I/S. The result of the integrationcalculation is multiplied by an integral gain factor K_(I). For example,if there is a residual error value e(t) after the application ofproportional control, the integral term I seeks to eliminate theresidual error by adding a control effect due to the historic cumulativevalue of the error. When the error is eliminated, the integral term Iceases to increase. This results in the proportional effect diminishingas the error decreases, but this is compensated for by the growingintegral effect. The derivative term D is a best estimate of the futuretrend of the error value e(t), based on its current rate of change. Thederivative term D is effectively seeking to reduce the effect of theerror by exerting a control influence generated by the rate of errorchange. The more rapid the change, the greater the controlling ordampening effect. The derivative term D is calculated by taking thederivative of the error values e(t) over time, indicated in. FIG. 3 asthe box labeled S, and multiplying the result by a derivative gainfactor K_(D). The control variable u(t) is calculated as the sum of theproportional term P, the integral term I, and the derivative term D. TheEXV controller 38 uses the value of the control variable u(t) toappropriately regulate the EXV 24.

PID control only utilizes measured temperature and pressure output fromthe evaporator, and as such this type of control is considered reactive,i.e. whatever changes in conditions are happening in the loop, thereaction to such condition changes is manifested at the output of theevaporator in the form of the temperature and pressure of therefrigerant, which is being measured and reacted to by adjusting the EXV24. This is not proactive, i.e. anticipating the need to adjust the EXV24 due to a change in conditions (load). In some embodiments, the EXVcontroller 38 also uses sensed compressor data, e.g. start-up state,change in rps, and sensed outdoor temperature, which provide indicationsof change in conditions, and as such can be used for proactive control.Such proactive control is referred to as feed-forward (FF) control. Asapplied to the HVAC system and corresponding EXV control describedherein, feed-forward refers to sensed data related to a change in one ormore operating characteristics (change in compressor state, e.g. startup or rps change) or external conditions (change in outside temperature)that will disturb the state of the HVAC system. Examples of suchdisturbances include, but are not limited to, load changes, compressorrps change, and compressor start-up. FF control provides a mechanism forreducing the effects of disturbances on the HVAC system. FF controlenables the HVAC system to respond faster and smoother during adisturbance (e.g. compressor speed variations) and reduce the number ofiterations that the EXV needs to adjust to achieve the desiredsuperheat. Reducing the number of iterations saves time and energyconsumption, and eventually increases the life of the EXV because offewer opening/closing operations, which improves reliability of thecomponent and the HVAC system. Feed-forward variables and correspondingsensed data can also include the speed and air flow changes of indoorand outdoor fans in the system if such changes are independent ofcompressor speed change. In the exemplary embodiments described below,compressor speed (rps) and indoor/outdoor fan speeds are interrelated,i.e. changes in compressor rps automatically change the indoor/outdoorfan speeds. It is understood that the description herein can be expandedto take into account other feed-forward variables. The feed-forwardsensed data is provided to the EXV controller to determine anticipatedchanges of state (conditions) related to the sensed data and appropriateEXV operating parameters for maintaining a current superheat set point.In an HVAC system using only feed-forward control, the control variableadjustment, e.g. adjustment of the EXV, is not error-based. Instead itis based on knowledge about the process in the form of a mathematicalmodel of the process (mapping), stored within and accessed by the EXVcontroller, and knowledge about, or measurements of, the processdisturbances, e.g. the feed-forward sensed data. To mitigate thecoupling between compressor speed and superheat, feed-forward control isused to reduce the effect of system disturbances, e.g. load changeand/or compressor rps change.

A master control algorithm executed by the EXV controller 38 canselectively utilize both PID control and feed-forward control. FIG. 4illustrates a functional block diagram of an algorithm utilizing bothPID control and feed-forward control according to some embodiments. ThePID control is implemented as in FIG. 3 , generally represented by thebox labeled “PID” in FIG. 4 . The feed-forward control and correspondingfeed-forward data are indicated generally by the box labeled “GFF”. ThePID control results u(t) and the feed-forward control results y(t) areapplied to a mapping procedure, described in greater detail below, togenerate a control signal z(t) that is provided to the EXV 24. Selectiveuse of both PID control and feed-forward control enables the EXVcontroller 38 to more quickly regulate the EXV 24 to achieve the desiredsuperheat as compared to only using PID control. This leads to improvedefficiency (less energy consumption), improved lifetime of the EXV, andso on.

There are three modes of operation that can be identified. A first modeis a start-up mode, which refers to when the HVAC system is turned on.Turning on the HVAC system also corresponds to turning on thecompressor, and as such the start-up mode also refers to when thecompressor is turned on. A second mode is a rps change mode, whichrefers to a change in speed of the compressor (compressor motor). Thisis particularly applicable to multiple-speed compressors. A third modeis a load change mode, which refers to a change in the load. Load change(or “just load change”) refers to the gradual/slow HVAC equipment loadchange which does not require a change in compressor speed (rps) toaddress. These situations are compensated for by the EXV opening andclosing to provide more or less refrigerant to the system in order tomatch the equipment capacity with the building load. Changes in thebuilding load are typically slow (gradual) and typically occur due togradual outdoor conditions changes (e.g. ambient temperature andhumidity increase or decrease which change the cooling or heating loadin the building) and/or gradual indoor condition changes such as morelatent heat inside the space (e.g. more people, cooking in the building,turn on electronic devices such as TV, computer, opening the externaldoors or windows, etc.). The load change mode, also referred to as “justload change” mode, only changes the position of EXV valve (more open orclose) to adjust the equipment load. It does not change the compressorspeed/rps. The rps change mode is activated when the HVAC systemcontroller decides that the compressor rps needs to be changed to adjustthe load. In this case a system control algorithm executed by the HVACsystem controller decides that EXV opening/closing is not enough tomatch the equipment and building loads and the compressor needs tochange the speed of rps order to change refrigerant flow momentarily.Variable speed compressors typically have multiple different operatingsettings, e.g. settings 1-8, where each setting has a corresponding rps.The rps change associated with the rps change mode corresponds to changein rps due to a change in the compressor operating setting.

The master control algorithm used by the EXV controller 38 includes aplurality of separate sub-control algorithms. Each of the three modes ofoperation utilize a unique subset of the sub-control algorithms. Themaster control algorithm includes an initial series of branchingdecision points to determine the current mode of operation and toexecute the select sub-control algorithms corresponding to the currentmode of operation, while not executing the sub-control algorithmscorresponding to the other two modes of operation. In this manner, theEXV controller 38 is enabled to more efficiently and quickly execute themaster control algorithm by only executing those sub-control algorithmscorresponding to the current mode of operation. The initial series ofbranching decision points are repeatedly evaluated to determine if thereis a change in the current mode of operation, and if a change isdetermined, the sub-control algorithms corresponding to the newlydetermined mode of operation are executed instead of the sub-controlalgorithms corresponding to the previously determined mode of operation.The initial branching decision points can be repeated every 0.5 to 3minutes, for example, after completion of each master control algorithmiteration. Such a time frame is subject to change or fin-tuning.Conceptually, the three modes can be considered parallel modes ofoperation and the corresponding sub-control algorithms associated witheach mode can be considered parallel processes, or paths through themaster control algorithm, where only one mode/process is being executedwhile the other two modes/processes are bypassed. In contrast, a mastercontrol algorithm configured as a series of processes would implementeach of the sub-control algorithms sequentially, in-series, requitingeach of the sub-control algorithms to be loaded into memory and executedin-series to determine their relevance (relevance based on current modeof operation versus the mode of sub-control algorithm) regardless of theactual current mode of operation. Configuring the master controlalgorithm with parallel processes improves the speed of EXV control andreduces complexity of the EXV controller 38. The master controlalgorithm with parallel processes provides an up-front mechanism forselecting which sub-control algorithms are to be executed based on adetermined current mode of operation.

Additionally, or alternatively, to implementing parallel modes ofoperation, the master control algorithm selectively implements eitherPID control and/or feed-forward control for regulating the EXV 24. PIDcontrol of the EXV 24 is conceptually reactive (feedback) based on thesensed temperature and pressure output from the evaporator 12, andfeed-forward control provides proactive control of the EXV 24 based onthe sensed outdoor temperature and compressor characteristics. Use offeed-forward control along with PID control provides improved energyconsumption of the HVAC system and increases the operational lifetime ofthe EXV by reducing the frequency of opening and closing of the EXV 24.

FIG. 5 illustrates a master control algorithm according to someembodiments. At the step 48, the master control algorithm starts and isinitialized. At the step 50, it is determined if the compressor isturned on. If the compressor is turned on, then the algorithm moves tothe step 52. If the compressor is not turned on, then the algorithmcontinues to monitor if the compressor is turned on. At the step 52, itis determined if a compressor start-up condition is present. If thecompressor start-up condition is not determined at the step 52, then thealgorithm moves to the step 54. If the compressor start-up condition isdetermined at the step 52, then the algorithm moves to the step 56.Determination that the start-up condition is present corresponds to thestart-up mode of operation, which begins at the step 56. At the step 56,the EXV is opened to a start-up position, which can be a defaultpercentage, such as 50% open, or a default step position. The EXV can bestep-wise opened and closed, and the EXV is controllable within a rangeof controllable steps. The default step position corresponds to aspecific step within the range of steps. At the step 58, the currentsuperheat is calculated using, the sensed temperature and pressure ofthe refrigerant at the output of the evaporator 12. At the step 64, itis, determined if a difference between the current superheat calculatedat the step 58 and the superheat set point is within a predefinedthreshold value. In some embodiments, the superheat set point is set toa value between 6 and 16 degrees, and the predefined threshold value towhich the start-up fast SH control algorithm adjusts the superheat iswithin 5 degrees of the superheat set point, for example the super heatset point is set at 10 degrees and the predefined threshold value is setto +/−5 degrees so that the absolute predefined superheat range is 5-15degrees (+/−5 degrees of 10 degree superheat set point). It isunderstood that the superheat set point range can be different than 6 to16 degrees, the superheat set point can be different than 10 degrees,and the predefined threshold value of the superheat for the start-upfast SH control algorithm can be larger or smaller than 5 degrees. If itis determined that the calculated current superheat is not within thepredefined threshold value at the step 64, then the algorithm moves tothe step 66 and the start-up fast SH control algorithm is executed. Ifit is determined that the calculated current superheat is within thepredefined threshold value at the step 64, then the algorithm moves tothe step 68. At the step 68, a fine SH control algorithm is executed.Steps 56, 58, 64, 66, and 68 correspond to the start-up mode ofoperation, and the start-up fast SH control algorithm 66 and the fine SHcontrol algorithm 68 are sub-control algorithms associated with thestart-up mode of operation.

At the step 54, it is determined if there is a change in the compressorrps. In some embodiments, the change in compressor rps corresponds to achange in compressor rps due to a change in the compressor operatingsetting. If it is determined at the step 54 that there is not a rpschange, then the algorithm moves to step 74. If it is determined at thestep 54 that there is a rps change, then the algorithm moves to step 69.At the step 69, the current superheat is calculated using the sensedtemperature and pressure of the refrigerant at the output of theevaporator 12. At the step 70, the current superheat calculated at thestep 69 is compared to the superheat set point, and it is determined ifthe calculated current superheat is within a predefined threshold valueof the superheat set point in a manner similar to that at the step 64.It is understood that the predefined threshold value used at the step 70can be different than the predefined threshold value used at the step64. If it is determined that the calculated current superheat is notwithin the predefined threshold value at the step 70, then the algorithmmoves to the step 72 and the rps change fast SH control algorithm isexecuted. If it is determined that the calculated current superheat iswithin the predefined threshold value at the step 70, then the algorithmmoves to the step 68. Steps 69, 70, 72, and 68 correspond to the rpschange mode of operation, and the rps change fast SH control algorithm72 and the fine SH control algorithm 68 are sub-control algorithmsassociated with the rps change mode of operation.

At the step 74, the current superheat is calculated using the sensedtemperature and pressure of the refrigerant at the output of theevaporator 12. At the step 76, the current superheat calculated at thestep 74 is compared to the superheat set point, and it is determined ifthe calculated current superheat is within a predefined threshold valueof the superheat set point in a manner similar to that at the step 64.It is understood that the predefined threshold value used at the step 76can be different than the predefined threshold value used at the step64. If it is determined that the calculated current superheat is notwithin the predefined threshold value at the step 76, then the algorithmmoves to the step 80 and the load change fast SH control algorithm isexecuted. If it is determined at the step 76 that the calculated currentsuperheat is within the predefined threshold value at the step 76, thenthe algorithm moves to the step 68 where the fine SH control algorithmis executed. Steps 74, 76, 80, and 68 correspond to the load change modeof operation, and the load change fast SH control algorithm 80 and thefine SH control algorithm 68 are sub-control algorithms associated withthe load change mode of operation.

In the exemplary master control algorithm shown in FIG. 5 , there arefour separate sub-control algorithms: start-up fast SH (superheat)control algorithm 66, fine SH control algorithm 68, rps change fast SHcontrol algorithm 72, and load change fast SH control algorithm 80. Theterm “fast” in the context of the sub-control algorithms 66, 72, 80refers to a “coarse” level of control, in contrast to the “fine” levelof control implemented in fine SH control algorithm 68. For example, ifthe superheat set point is 10 degrees, but the actual calculatedsuperheat is 30 degrees, then the fast sub-control algorithms 66, 72, 80each function to drop the superheat to within a few degrees, such aswithin 5 degrees, of the superheat set point. The fine SH controlalgorithm 68 then functions to drop the superheat by the few degrees toabout the superheat set point, such as 10 degrees. In this manner, thefast sub-control algorithms function as coarse control mechanisms(coarse-tuning) and the fine sub-control algorithm functions as a finecontrol mechanism (fine-tuning).

FIG. 6 illustrates the start-up fast SH control algorithm of FIG. 5according to some embodiments. At the step 82, the current superheat iscalculated using the sensed temperature and pressure of the refrigerantat the output of the evaporator 12. At the step 84, it is determined ifthe measured temperature (Tsat) and pressure (Psat) at the output of theevaporator is below a normal lower operating threshold. In someembodiments, the normal lower operating threshold for the pressure is15-20 psi and the normal lower operating range for the temperature is−26 F (corresponding to 15 psi) to −35 F (corresponding to 20 psi). Ifit is determined at the step 84 that either the temperature or pressureis below the normal lower operating threshold, then the algorithm movesto the step 86 where an error signal is generated. If it is determinedat the step 84 that both the temperature and pressure are within thenormal operating range, then the algorithm moves to the step 87. At thestep 87, it is determined if the compressor has been turned off. If itis determined that the compressor has been turned off at the step 87,then at the step 89 the EXV is closed and the algorithm moves back tothe step 48. If it is determined that the compressor has not been turnedoff at the step 87, then at the step 88 a start-up mode EXV stepadjustment calculation is made. In some embodiments, both a PID controland feed-forward control are performed during this step. Thefeed-forward (FF) control uses a mapping and conversion procedure, whichis different when used in the start-up mode verses the rps change mode.The FF control used in the start-up (SU) mode is designated by “FF-SU”,to contrast the FF control used in the rps change mode, designated assimply “FF” (FIG. 7 ). The PID control is performed using the measuredtemperature and pressure output from the evaporator.

The PID control also uses the proportional gain factor K_(P), theintegral gain factor K_(I), and the derivative gain factor K_(P). ThePID control implemented as part of the start-up fast SH controlalgorithm 66 uses gain factor values specifically determined for thestart-up fast SH control algorithm. As such, the PID control used instep 88 is referred to as PID3 control, and the specific gain factorvalues used by PID3 control are referred to as the proportional gainfactor K_(P3), the integral gain factor K_(I3), and the derivative gainfactor K_(P3). Similarly, PID control used in other sub-controlalgorithms, such as the rps change fast SH control algorithm 72, theload change fast SH control algorithm 80, and the fine SH controlalgorithm 68, also use gain factor values specifically determined fortheir respective sub-control algorithms. For example, the PID controlused in the rps change fast SH control algorithm 72 (FIG. 7 ) isreferred to as PID2 control, and the specific gain factor values used byPID2 control are referred to as the proportional gain factor K_(P2), theintegral gain facto K_(I2), and the derivative gain factor K_(P2). ThePID control used in the load change that SH control algorithm 80 (FIG. 8) is referred to as PID1 control, and the specific gain factor valuesused by PID1 control are referred to as the proportional gain factorK_(P1), the integral gain factor K_(I1), and the derivative gain factorK_(P1). The PID control used in the fine SH control algorithm 68 (FIG. 9) includes two separate PID controls, referred to as PID4 control andPID5 control, where the specific gain factor values used by PID4 controlare referred to as the proportional gain factor K_(P4), the integralgain factor K_(I4), and doe derivative gain factor K_(P4), and thespecific gain factor values used by PID5 control are referred to as theproportional gain factor K_(P5), the integral gain factor K_(I5), andthe derivative gain factor K_(P5). The use of references PID1, PID2,PID3, PID4, and PID5 in FIGS. 6-9 refers to different values of the gainfactors K_(P), K_(I) and K_(D) used in the PID control. The specificgain factor values are predetermined constants stored in a look-uptable, for example, accessible by the master control algorithm. Forexample, the values of the gain factors K_(P), K_(I), and K_(D) used bythe sub-control algorithm for PID1 control are K_(P1), K_(I1), andK_(D1), etc. The specific gain factor values are application specificand are typically different from one sub-control algorithm to the next.The specific gain factor values for each sub-control algorithm aredifferent due to the different modes of operation associated with eachsub-control algorithm. The specific gain factor values can be different,similar, or the same from one sub-control algorithm to the next due tothe modes of operation, outdoor/indoor conditions, and the location ofPID control within the master control algorithm. In addition, thespecific gain factor values depend on the superheat set point and thetime target for which the master control algorithm is configured toadjust to this superheat set point. In some embodiments, the specificgain factor values for each sub-control algorithm are determined duringcalibration of the HVAC system in a laboratory setting.

The FF control is performed using the measured outdoor temperature andcompressor characteristics, e.g. start-up condition or rps change. Insome embodiments, mapping and conversion procedure is performed usingthe results of the feed-forward control and the PID3 control todetermine a corresponding start-up mode EXV step adjustment. The EXV 24is adjusted according to the determined start-up mode EXV stepadjustment. In some embodiments, initially the feed-forward controlFF-SU is implemented using a working map corresponding to the regulatingdevice (EXV). This map is the opening step of the EXV as a function ofsystem operating conditions including, for example, outdoor temperature,compressor speed (rps), indoor fan speed (rpm), and outdoor fan speed(rpm). In some embodiments, the map is a look up table that provides aspecific step count for the EXV corresponding to specific systemoperating condition values. Feed-forward mapping relates the HVAC systeminformation, such as outdoor temperature and compressor rps, to aspecific EXV step or position. At each operating condition combination,e.g. a specific outdoor temperature and specific compressor rps (orstage), the feed-forward map specifies a step (or open position) for theEXV to be opened by its stepper motor without yet implementing PIDcontrol and trial and error. This EXV open/closed position is not thefinal position, but it is relatively close to the final position. Withfurther assistance from the associated PID control, e.g. FF-SU+PID3, theEXV step position is fine tuned to the final position much quicker thanonly implementing PID control. In this sense, the feed-forward controlFF-SU functions as fast, or coarse, tuning, and the PID3 controlfunctions as fine-tuning. In general, feed-forward control adjusts thesuperheat as close as possible to the range of target with minimum EXVposition/step change at the shortest amount of time. In someembodiments, implementation of the feed-forward control FF-SU may besufficient for adjusting the superheat value to within a predeterminedthreshold value, such as determined at either the steps 90 or 94, inwhich case it may not be necessary to implement the PID3 control. Inthis case the PID3 control can be bypassed. In this manner, the PID3control can be utilized as a back-up procedure in case the feed-forwardcontrol FF-SU alone does not adjust the superheat to within thepredetermined range.

After the EXV step adjustment is determined and executed at the step 88,the current superheat is again calculated using the sensed temperatureand pressure of the refrigerant at the output of the evaporator 12, andthe newly calculated current superheat is compared to the superheat setpoint at the step 90. If it is determined at the step 90 that thecurrent superheat is equal to or approximate to the superheat set point,such as equal to or less than 1 degree of the superheat set point, thenit is determined that the EXV is accurately set and the algorithm movesto the step 92 where the EXV is held at the current step. It isunderstood that the “approximate” determination of how close the newlycalculated current superheat is to the superheat set point can begreater or less than the 1 degree range described above. The start-upfast SH control algorithm ends at the step 92, and the master controlalgorithm restarts at the step 48 after a predefined time period. If itis determined at the step 90 that the current superheat is not equal toor approximate to the superheat set point, then it is determined at thestep 94 if the newly calculated current superheat is within a predefinedthreshold value in a manner similar to that at the step 64 (FIG. 5 ). Itis understood that the predefined threshold value used at the step 94can be different than the predefined threshold value used at the step64. If it is determined at the step 94 that the newly calculated currentsuperheat is not within the predefined threshold value, then thealgorithm moves back to the step 84. If it is determined at the step 94that the newly calculated current superheat is within the predefinedthreshold value, then the algorithm moves to the step 68 where the fineSH control algorithm is executed.

FIG. 7 illustrates the rps change fast SH control algorithm of FIG. 5according to some embodiments. At the step 96, the current superheat iscalculated using the sensed temperature and pressure of the refrigerantat the output of the evaporator 12. At the step 98, it is determined ifthe measured temperature (Tsat) and pressure (Psat) at the output of theevaporator is outside of the normal operating range. If it is determinedat the step 98 that either the temperature or pressure is outside thenormal operating range, then the algorithm moves to the step 100 wherean error signal is generated. If it is determined at the step 98 thatboth the temperature and pressure are within the normal operating range,then the algorithm moves to the step 101. At the step 101, it isdetermined if the compressor has been turned off. If it is determinedthat the compressor has been turned off at the step 101, then at thestep 103 the EXV is closed and the algorithm moves back to the step 48.If it is determined that the compressor has not been turned off at thestep 101, then at the step 102 a rps change mode EXV step adjustmentcalculation is made. In some embodiments, both a PID2 control and FFcontrol are performed during this step. The PID2 control is performedusing the measured temperature and pressure output from the evaporator,as well as using the proportional gain factor K_(P2), the integral gainfactor K_(I2), and the derivative gain factor K_(P2).

The feed-forward control is performed using the measured outdoortemperature and compressor characteristics, e.g. start-up condition orrsp change. In some embodiments, mapping and conversion procedure isperformed using the results of the PID2 control and feed-forward controlto determine a corresponding rps change mode EXV step adjustment. TheEXV 24 is adjusted according to the determined rps change mode EXV stepadjustment. After the EXV step adjustment is determined and executed atthe step 102, the current superheat is again calculated using the sensedtemperature and pressure of the refrigerant at the output of theevaporator 12, and the newly calculated current superheat is compared tothe superheat set point at the step 104. If it is determined at the step104 that the current superheat is equal to or approximate to thesuperheat set point, such as equal to or less than 1 degree of thesuperheat set point, then it is determined that the EXV is accuratelyset and the algorithm moves to the step 106 where the EXV is held at thecurrent step. It is understood that the “approximate” determination ofhow close the newly calculated current superheat is to the superheat setpoint can be greater or less than the 1 degree range described above.The rps change fast SH control algorithm ends at the step 106, and themaster control algorithm restarts at the step 48 after a predefined timeperiod. If it is determined at the step 104 that the current superheatis not equal to or approximate to the superheat set point, then it isdetermined at the step 108 if the newly calculated current superheat iswithin a predefined threshold value in a manner similar to that at thestep 64 (FIG. 5 ). It is understood that the predefined threshold valueused at the step 104 can be different than the predefined thresholdvalue used at the step 64. If it is determined at the step 108 that thenewly calculated current superheat is not within the predefinedthreshold value, then the algorithm moves back to the step 98. If it isdetermined at the step 108 that the newly calculated current superheatis within the predefined threshold value, then the algorithm moves tothe step 68 where the fine SH control algorithm is executed.

Feed-forward control is generally used to inform the master controlalgorithm ahead of time when there are abrupt refrigerant conditionchanges in the HVAC system (which is called disturbance into the system)and the EXV has not yet been adjusted to compensate for such conditionchanges. These conditions include compressor start up (start-up mode)and compressor speed change (rps change mode). In the case of “just loadchange”, there is no disturbance and there is only gradual changing ofthe system load with gradual outdoor (or maybe indoor) temperaturechanges. In these cases, there is no abrupt refrigerant flow change inthe system and there is no information to “feed forward” to the mastercontrol algorithm and EXV controller regarding the status of refrigerantflow. Therefore, the EXV can gradually open or close its position with asimple PID control to keep the current superheat close to the superheatset point FIG. 8 illustrates the load change first SH control algorithmof FIG. 5 according to some embodiments. At the step 110, the currentsuperheat is calculated using the sensed temperature and pressure of therefrigerant at the output of the evaporator 12. At the step 112, it isdetermined if the measured temperature (Tsat) and pressure (Psat) at theoutput of the evaporator is outside of the normal operating range. If itis determined at the step 112 that either the temperature or pressure isoutside the normal operating range, then the algorithm moves to the step114 where an error signal is generated. If it is determined at the step112 that both the temperature and pressure are within the normaloperating range, then the algorithm moves to the step 115. At the step115, it is determined if the compressor has been turned off. If it isdetermined that the compressor has been turned off at the step 115, thenat the step 117 the EXV is closed and the algorithm moves back to thestep 48. If it is determined that the compressor has not been turned offat the step 115, then at the step 116 a load change mode EXV stepadjustment calculation is made. In some embodiments, a PID1 control isperformed during this step. The PID1 control is performed using themeasured temperature and pressure output from the evaporator, as well asusing the proportional pin factor K_(P1), the integral gain factorK_(I1), and the derivative gain factor K_(P1).

Execution of the PID1 control results in a corresponding load changemode EXV step adjustment. The EXV 24 is adjusted according to thedetermined load change mode EXV step adjustment. After the load changemode EXV step adjustment is determined and executed at the step 116, thecurrent superheat is again calculated using the sensed temperature andpressure of the refrigerant at the output of the evaporator 12, and thenewly calculated current superheat is compared to the superheat setpoint at the step 118. If it is determined at the step 118 that thecurrent superheat is equal to or approximate to the superheat set point,such as equal to or less than 1 degree of the superheat set point, thenit is determined that the EXV is accurately set and the algorithm movesto the step 120 where the EXV is held at the current step. It isunderstood that the “approximate” determination of how close the newlycalculated current superheat is to the superheat set point can begreater or less than the 1 degree range described above. The load changefast SH control algorithm ends at the step 120, and the master controlalgorithm restarts at the step 48 after a predefined time period. If itis determined at the step 118 that the current superheat is not equal toor approximate to the superheat set point, then it is determined at thestep 122 if the newly calculated current superheat is within apredefined threshold value in a manner similar to that at the step 64(FIG. 5 ). It is understood that the predefined threshold value used atthe step 122 can be different than the predefined threshold value usedat the step 64. If it is determined at the step 122 that the newlycalculated current superheat is not within the predefined thresholdvalue, then the algorithm moves back to the step 112. If it isdetermined at the step 122 that the newly calculated current superheatis within the predefined threshold value, then the algorithm moves tothe step 68 where the fine SH control algorithm is executed.

FIG. 9 illustrates the fine SH control algorithm of FIG. 5 according tosome embodiments. In some embodiments, the fine SH control algorithmuses only PID control. In some embodiments, there are two PID controlsteps in the fine SH control algorithm, namely PID4 control and PID5control. PID4 control is the main loop PID in the fine-tuning procedureperformed by the fine SH control algorithm, which is subject to alimited steps or time. In an exemplary procedure, the fine SH controlalgorithm is limited to 3-4 minutes. It is understood that the fine SHcontrol algorithm can be configured to run for more, or less, than 3-4minutes. PID5 control is a back-up control algorithm used to make surethat with an aggressive gain set (gain factor values), the fine SHcontrol algorithm can lower the superheat to within the set targetrange, e.g. within 1 degree of the superheat set point, without sendingthe master control algorithm back to a previous fast-tuning stage, suchas sub-control algorithms 88, 102, 116. If after implementation of thePID5 control the superheat is not within the set target range, then thealgorithm returns back to a previous fast-tuning stage. In someembodiments, the fine SH control algorithm is implemented with only asingle PID control, such as PID4 control.

The fine SH control algorithm is used to adjust the current superheat tobe equal to or nearly equally to the superheat set point, i.e. withinthe set target range. At the step 124, a total TLC is compared to apredefined TLC threshold value. The total TLC is the time or number ofiterations that the algorithm loop is actually executed. Limiting theexecution time or number or iterations to a finite amount prevents thealgorithm from continuing indefinitely. It is understood that similartime or iteration constraints can be implemented within the othersub-control algorithms. If the total TLC is below the TLC thresholdvalue, then the algorithm moves to the step 126. If the total TLC isequal to or greater than the threshold value, then the algorithm movesto the step 128. At the step 126, a first fine-tuned EXV step adjustmentcalculation is made. In some embodiments, a PID4 control is performedduring this step. The PID4 control is performed using the measuredtemperature and pressure output from the evaporator, as well as usingthe proportional gain factor K_(P4), the integral gain factor K_(I4),and the derivative gain factor K_(P4). After the first fine-tuned EXVstep adjustment is determined and executed at the step 126, thealgorithm moves back to the step 124. The EXV 24 is adjusted accordingto the determined first fine-tuned EXV step adjustment.

At the step 128, an optional second fine-tuned EXV step adjustmentcalculation is made. In some embodiments, a PID control is performedduring this step. The PID5 control is performed using the measuredtemperature and pressure output from the evaporator, as well as usingthe proportional gain factor K_(P5), the integral gain factor K_(I5),and the derivative gain factor K_(P5). After the second fine-tuned EXVstep adjustment is determined and executed at the step 128, thealgorithm moves to the step 130. The EXV 24 is adjusted according to thedetermined second fine-tuned EXV step adjustment.

After the second fine-tuned EXV step adjustment is determined andexecuted at the step 128, the current superheat is again calculatedusing the sensed temperature and pressure of the refrigerant at theoutput of the evaporator 12, and the newly calculated current superheatis compared to the superheat set point at the step 130 to determine if adifference between the newly calculated current superheat and thesuperheat set point is within a predefined threshold value in a mannersimilar to that described in step 64 (FIG. 5 ). In some embodiments,this predefined threshold value is 5 degrees. It is understood that thepredefined threshold value can be larger or smaller than 5 degrees. Ifit is determined at the step 130 that the newly calculated currentsuperheat is not within the predefined threshold value, then thealgorithm moves back to the step 116 (FIG. 8 ) and a load change modeEXV step adjustment is again calculated and executed. The algorithmmoves to the sub-control algorithm 116 instead of to the othersub-control algorithms 88 or 102 because once the master controlalgorithm reaches the fine SH control algorithm 68 it is assumed thatthere are no longer disturbances related to the start-up mode or the rpschange mode. As such, the sub-control algorithm 88 related to the loadchange mode suffices for adjusting the superheat to within theacceptable range of the superheat set point. If it is determined at thestep 130 that the newly calculated current superheat is within thepredefined threshold value, then the algorithm moves to the step 132. Atthe step 132, the current superheat is compared to the superheat setpoint. If it is determined at the step 132 that the current superheat isequal to or approximate to the superheat set point, such as equal to orless than 1 degree of the superheat set point, then it is determinedthat the EXV is accurately set and the algorithm moves to the step 134where the EXV is held at the current step. It is understood that the“approximate” determination of how close the newly calculated currentsuperheat is to the superheat set point can be greater or less than the1 degree range described above. The fine SH control algorithm ends atthe step 134, and the master control algorithm restarts at the step 48after a predefined time period. If it is determined at the step 132 thatthe current superheat is not equal to or approximate to the superheatset point, then the algorithm moves back to the step 124.

In some embodiments, a primary function of the FF control is to provideadjustments to the EXV in response to disturbances in the HVAC system.FF control makes EXV adjustments related to system disturbances, e.g.compressor speed change, more efficiently (faster) than PID control. Insome embodiments, this disturbance handling by FF control enables theHVAC system to respond faster by utilizing look up tables (mapping). Inthis sense, the FF control provides coarse-tuning. In some embodiments,PID control provides fine-tuning through proper gain factor values.However, the gain factor values used by PID control can be set foreither fine-tuning or coarse tuning. For example, different gain factorvalues for PID1 control versus PID4 control or PID5 control makes thetuning performed by PID1 control more coarse.

In the embodiments described above, the sensed outdoor temperature andcompressor characteristics are implemented as part of sub-controlalgorithms 66 and 72 that utilize feed-forward control. These fast(coarse-tuning) sub-control algorithms 66, 72 utilize the sensedpressure and temperature values for PID control and sensed outdoortemperature and compressor characteristics for feed-forward control,along with a sub-algorithm specific map that provides an amount of“step” for adjusting the EXV 24, e.g. step the EXV open or closed by thestep and direction (positive for open, negative for closed) indicated bythe map, or that provides a step value at which the EXV is to be set.Essentially, the sensed data (both for PID control and feed-forwardcontrol) is used by the EXV controller 38 to determine the EXV step(amount that the EXV is open) to be moved to and eventually held at oncethe system reaches an equilibrium state based on the measuredconditions. It is understood that alternative embodiments are alsocontemplated. In other embodiments, only PID control can be used in eachof the sub-control algorithms. In such embodiments, the sub-controlalgorithms 66 and 72 do not utilize feed-forward control. The gainfactors used by the PID control in these modified sub-control algorithms66, 72 use different values then the sub-control algorithms 66, 72 thatuse both feed-forward control and PID control. The mapping functionsused in the sub-control algorithms 66, 72 to determine the appropriatecontrol signal for the EXV 24 are also different when using only PIDcontrol. In still other embodiments, the sub-control algorithms 66, 72are alternatively modified so as to only implement feed-forward control.In such embodiments, the sub-control algorithms 66 and 72 do not utilizePID control. The mapping functions used in the sub-control algorithms66, 72 to determine the appropriate control signal for the EXV 24 arealso different when using only feed-forward control.

The present application has been described in terms of specificembodiments incorporating details to facilitate the understanding of theprinciples of construction and operation of the EXV control system. Manyof the components shown and described in the various figures can beinterchanged to achieve the results necessary, and this descriptionshould be read to encompass such interchange as well. As such,references herein to specific embodiments and details thereof are notintended to limit the scope of the claims appended hereto. It will beapparent to those skilled in the art that modifications can be made tothe embodiments chosen for illustration without departing from thespirit and scope of the application.

1-8. (canceled)
 9. A heating, ventilation, and air condition (HVAC)system, comprising: a refrigerant loop including a refrigerant flowingwithin; a compressor coupled to the refrigerant loop; an evaporatorcoupled to the refrigerant loop; an electronic expansion valve coupledto the refrigerant loop to regulate a mass flow of the refrigerant intothe evaporator; and a controller coupled to the compressor and theelectronic expansion valve, wherein the controller is configured toreceive data signals corresponding to one or more compressorcharacteristics, wherein the controller includes and is configured toexecute a master control algorithm to generate control signals forcontrolling the electronic expansion valve, wherein the master controlalgorithm comprises a plurality of sub-control algorithms, and whereinthe master control algorithm is configured to selectively execute asubset of the plurality of sub-control algorithms depending on adetermined current operating mode.
 10. The HVAC system of claim 9wherein the HVAC system further comprises a temperature sensor forsensing an external temperature, and the data signals received by thecontroller further include an external temperature value.
 11. The HVACsystem of claim 10 wherein the master control algorithm includes afeed-forward sub-control algorithm that generates a step adjustment ofthe electronic control valve based on the one or more compressorcharacteristics to proactively adjust the electronic control valve, andfurther wherein the feed-forward sub-control algorithm generates thestep adjustment based on the one or more compressor characteristics andthe external temperature value.
 12. The HVAC system of claim 11 whereinthe master control algorithm comprises a plurality of sub-controlalgorithms, the feed-forward sub-control algorithm is one of theplurality of sub-control algorithms.
 13. The HVAC system of claim 12,wherein the current operating mode is determined according to thecompressor characteristics.
 14. The HVAC system of claim 13 wherein thecurrent operating mode is one of a start-up mode, a compressor rpschange mode, and a load change mode.
 15. The HVAC system of claim 14wherein the subset of the plurality of sub-control algorithmscorresponding to the start-up mode includes a first feed-forward controlalgorithm, a first PID (Proportional Integral Derivative) controlalgorithm, and a second PID control algorithm.
 16. The HVAC system ofclaim 15 wherein the master control algorithm is configured to executethe first feed-forward control algorithm to provide a coarse-tuned firstelectronic expansion valve step adjustment, then to execute the firstPID control algorithm to provide a fine-tuned second electronicexpansion valve step adjustment, and then to execute the second PIDcontrol algorithm to provide a fine-tuned third electronic expansionvalve step adjustment.
 17. The HVAC system of claim 16 wherein the firstPID control algorithm applies first gain factor values and the secondPID control algorithm applies second gain factor values different fromthe first gain factor values.
 18. The HVAC system of claim 15 whereinthe subset of the plurality of sub-control algorithms corresponding tothe compressor rps change mode includes a second feed-forward controlalgorithm, a third PID control algorithm, and the second PID controlalgorithm.
 19. The HVAC system of claim 18 wherein the master controlalgorithm is configured to execute the second feed-forward controlalgorithm to provide a coarse-tuned first electronic expansion valvestep adjustment, then to execute the third PID control algorithm toprovide a fine-tuned second electronic expansion valve step adjustment,and then to execute the second PID control algorithm to provide afine-tuned third electronic expansion valve step adjustment.
 20. TheHVAC system of claim 19 wherein the second PID control algorithm appliessecond gain factor values and the third PID control algorithm appliesthird gain factor values different from the second gain factor values.21. The HVAC system of claim 18 wherein the subset of the plurality ofsub-control algorithms corresponding to the load change mode includes afourth PID control algorithm and the second PID control algorithm. 22.The HVAC system of claim 21 wherein the master control algorithm isconfigured to execute the fourth PID control algorithm to provide afine-tuned first electronic expansion valve step adjustment and then toexecute the second PID control algorithm to provide a fine-tuned secondelectronic expansion valve step adjustment.
 23. The HVAC system of claim9 wherein the data signals received by the controller further include apressure value at an output of the evaporator and a temperature value atthe output of the evaporator.
 24. The HVAC system of claim 23 whereinthe controller is further configured to execute a PID control algorithmusing the received pressure value and the received temperature value toadjust the electronic expansion valve.
 25. The HVAC system of claim 24wherein the master control algorithm is configured to first execute thefeed-forward control algorithm followed by the PID control algorithm.